Communication partners which are respectively in transmitting and receiving communication with each other only for a short time and the methods of operating them are known in the state of the art in particular where a small available transmitting band width has to be distributed to a large number of transmitters and receivers. As there is not just any amount of transmitting band width available, the communication subscribers must manage therewith efficiently. Thus national and international standards for given permitted frequency bands prescribe the so-called listen-before-transmit method (LBT), in accordance with which any communication subscriber wishing to transmit in the specified frequency band must firstly observe the transmitting traffic present before that subscriber himself may transmit, after a prescribed period of time in which there is no radio traffic in the frequency band. Usually in that case one communication subscriber remains in the receiving mode and waits for a recognition signal from the communication partner, which signals the readiness to receive a mutual communication.
Modern electromedical implants, in particular cardiac pacemakers defibrillators and the like, offer physician and patients a very high degree of security and comfort by what is referred to as home monitoring functions.
In that respect the implant protocols diagnosis and therapy information and transmits that information to a portable external patient device by way of a telemetry interface. From there the data are passed to the home monitoring service center where they are stored and displayed for the physician. In that way the physician can be informed directly about therapy progress and the current state of health of his patients. He thus enjoys the possibility of reacting quickly to changes in the state of health of his patients.
Without home monitoring the physician can obtain those items of information only in the context of an examination of the patient. In critical situations that results in unwanted delays in the flow of information. In addition any examination involves a considerable amount of time for the patient and the physician. Frequent examinations result in a restriction in terms of mobility and quality of life, in particular for the patient.
With home monitoring, the implant information is sent by way of the described technical apparatus (see also U.S. Pat. Nos. 6,553,262 and 5,752,976) in the background without the patient being limited in terms of leading a normal life; in other words, he has the security of physician home monitoring without the stress caused by frequent examinations.
Indirect communication between an implant and a home monitoring service center is necessary for the reason that the implant can transmit only over a short distance once again by virtue of the strict demands in respect of power consumption. The short distance between the patient device and the electromedical implant also ensures that the transmission signal of the patient device, in spite of screening by the body of the patient, is sufficiently strong to be received by the implant.
In the case of such an electromedical implant which is disposed in the body of a patient however, the difficulty which arises is that the implant is screened by the surrounding body so that weak signals which just occupy the transmission channel cannot be perceived. The electromedical implant could thus wrongly view the transmission channel as being unused, claim it for itself and interfere with the communication of other devices. An LBT protocol cannot therefore be initiated by an electromedical implant, and for that reason a communication must always be initiated by the external patient device which is in a position to listen to the transmission channel with the necessary level of sensitivity.
Uninterrupted reception readiness on the part of the receiver also means an additional current requirement which is unacceptably high under some circumstances, for a battery-operated communication device. That applies in particular to electromedical implants such as for example a cardiac pacemaker which is placed in the body of a patient ready for operation over a number of years without the possibility of charging up or replacing the batteries. In the case of electromedical implants it would therefore be advantageous to be able also to continually switch off the receiver and to switch it on again only at the moments of the expected transmission on the part of the communication partner.
In order to guarantee the patient a freedom of movement which is as unrestricted as possible, the patient device in the form of a portable unit usually communicates with the home monitoring service center by way of a wireless data or telephone connection. As the operation of cellular radio devices is prohibited at numerous locations such as for example in hospitals or aircraft, a patient can be obliged to temporarily switch off the patient device.
A problem now however is that, after the patient device is switched on, the moment of the next reception cycle of the cardiac pacemaker is not known and the two devices therefore must provide for temporal matching to each other of their activity phases. That can also happen if the radio channel was in the meantime occupied by an outside device so that the cardiac pacemaker and the patient device could not communicate with each other. The above-indicated limitations in regard to use of the permitted frequency bands in question however impose tight limits as the receiving unit of the cardiac pacemaker cannot be continually switched on even after loss of contact with the patient device.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems and methods with the present invention as set forth in the remainder of the present application with reference to the drawings.